Imatinib in c‑KIT‑mutated metastatic solid tumors: A multicenter trial of Korean Cancer Study Group (UN18‑05 Trial)

Introduction: We conducted an open‑label, single‑arm, multi‑center phase II trial to evaluate the efficacy and safety of imatinib chemotherapy‑refractory or metastatic solid tumor patients with c‑KIT mutations and/or amplification. Methods: c‑KIT mutations and amplification were detected using NGS. Imatinib (400 mg daily) was administered continuously in 28‑day cycles until disease progression, unacceptable adverse events, or death by any cause. The primary endpoint was the objective response rate (ORR). Result: In total, 18 patients were enrolled on this trial. The most common tumor type was melanoma (n = 15, 83.3%), followed by ovarian cancer, breast cancer, and metastasis of unknown origin (MUO) (each n = 1, 5.5%). The total number of evaluable patients was 17, of which one patient had a complete response, six patients had partial response, and two patients had stable disease. The overall response rate (ORR) of 41.2% (95% CI 17.80–64.60) and a disease control rate of 52.9% (95% CI 29.17–76.63). The median progression‑free survival was 2.2 months (95% CI 1.29–3.20), and median overall survival was 9.1 months (95% CI 2.10–16.11). The most common adverse events were edema (31.3%), anorexia (25.0%), nausea (18.8%), and skin rash (18.8%). Conclusion: Imatinib demonstrated modest anti‑tumor activity and a manageable safety profile in chemotherapy‑refractory solid tumors with c‑KIT mutation, especially in melanoma patients.